Constraining the early universe with primordial black holes

TL;DR

This thesis investigates how non-Gaussianity and super-horizon modes influence primordial black hole abundance, significantly affecting constraints on early universe models and dark matter formation.

Contribution

It demonstrates the substantial impact of non-Gaussianity and modal coupling on PBH abundance constraints, refining early universe and dark matter models.

Findings

Small non-Gaussianity can alter PBH constraints by an order of magnitude.

Super-horizon modes have little direct effect on PBH formation.

Modal coupling to CMB-scale modes can exclude many PBH dark matter scenarios.

Abstract

In this thesis, the effect of non-Gaussianity upon the abundance of primordial black holes (PBHs), and the implications of such an effect are considered. It is shown that even small non-Gaussianity parameters can have a large effect on the constraints that can be placed on the primordial curvature perturbation power spectrum - which can become stronger or weaker by an order of magnitude. The effects of super-horizon curvature perturbation modes at the time of PBH formation are considered, and it is shown that these have little effect on the formation of a PBH, but can have an indirect effect on the abundance of PBHs due to modal coupling to horizon-scale modes in the presence of non-Gaussianity. By taking into account the effect of modal coupling to CMB-scale modes, many models can be ruled out as a mechanism to produce enough PBHs to constitute dark matter.